German Patent Application No. 23 39 896 describes an ignition output stage for internal combustion engines. This primary winding of the ignition coil is connected in series with the interrupter assembly of a switching transistor. The switching transistor is implemented as a Darlington circuit, with a Zener diode connected in parallel to the collector-base system. This Zener diode ensures that the voltage at the interrupter assembly of the switching transistor does not exceed a permissible value. High voltages that represent a danger to the switching transistor occur, in particular, during the transition of the switching transistor interrupter assembly into the off state and are generated by the high voltage transformed to the primary side.
If the collector-emitter voltage reaches the Zener voltage of the base-collector diode, a Zener current flows to the base of the ignition Darlington. This is again switched to the on state so in clamping operation, simultaneously a voltage is present and current flows until the ignition spark on the secondary side of the coil sparks over the coil and the rest of the coil energy flows into the spark gap.
The ignition coil of an ignition circuit is connected with rotating distribution over an ignition distributor to the corresponding ignition spark plug of the internal combustion engine or, with static distribution, directly to the spark plug. In this arrangement very large cable lengths occur between the individual connections, e.g., between the switching transistor and the ignition coil and between the switching transistor and ground and between the triggering circuit of the ignition Darlington and the base of the ignition Darlington. The ohmic resistances and inductances that are present because of the electric cable have an antenna effect, so that during the ignition process the base wiring of the switching transistor is supplied with weak parasitic base current which leads to the ignition voltage only slowly reaching the value necessary for ignition, since the switching transistor is somewhat notched up again by this parasitic current. This effect can be taken into account by using the shortest possible emitter and collector wires or by the use of shielded control wires for the switching transistor base.